The invention relates to coordination catalyst systems based on transition metal compounds of subgroups IV to VIII and organometallic compounds of main group III of the Periodic Table of the Elements. Such organometallic catalysts are extraordinarily versatile catalyst systems which are used in chemical reactions of and with olefinically unsaturated compounds. These are, in particular, processes for preparing olefin polymers by coordination polymerization and the metathesis of alkenes or alkynes. Of substantial industrial importance is the preparation of polyethylene, of increased density (high density polyethylene, (HDPE) and of polymers and copolymers of ethylene, propylene or other 1-alkenes and alkynes. Catalyzed metathesis enables higher unsaturated hydrocarbon compounds to be prepared in a targeted way from unsymmetric alkenes or alkynes and, from unsaturated cyclic hydrocarbon compounds, makes it possible to obtain long-chain unsaturated hydrocarbons. The latter are used, for example, in the preparation of elastomers. In addition, coordination catalysts are used in further reactions, such as in the hydrogenation of alkenes or in organometallic syntheses.
In accordance with the previous scientific knowledge of the mechanism of action of coordination catalysts, it is assumed that in each case one transition metal compound forms the catalytically active center to which the olefinically unsaturated compound binds coordinately in a first step. The olefin polymerization proceeds via a coordination of the monomers and a subsequent insertion reaction into a transition metal-carbon or a transition metal-hydrogen bond. The presence of organometallic compounds in the coordination catalyst systems or during the catalyzed reaction is required to activate the catalyst or maintain its activity by reduction, with or without alkylation or formation of a complex system. These compounds are therefore also known as co-catalysts. The compound containing the catalytically active transition metal atom is known as the primary catalyst or pre-catalyst.
The best known industrially used catalyst systems for coordination polymerization are of the "Ziegler-Natta catalyst" type and of the "Phillips catalyst" type. The former comprise the reaction product of a metal alkyl or hydride of the elements of the first three main groups of the Periodic Table and a reducible compound of a transition metal element of subgroups IV to VII, the combination most frequently used comprising an aluminum alkyl, such as triethylaluminum or diethylaluminum chloride, and titanium(IV) chloride. Newer highly active Ziegler-Natta catalysts are systems in which the titanium compound is chemically fixed to the surface of magnesium compounds such as, in particular, magnesium chloride.
As Phillips catalysts, use is made of chromium compounds which undergo reduction or activation principally by organometallic compounds and are bound to inorganic supports. Cr(VI) and Cr(II) are regarded as catalytically active species ("reduced Phillips catalyst"). Here too, the co-catalysts used are principally alkylaluminum compounds and also aluminoxane compounds.
Newer developments of particularly high-performance polymerization catalysts are based on metallocene compounds. The catalysts known as "Kaminsky catalysts" are, for example, titanocene and zircononocene compounds which are cyclopentadienyl complexes of titanium or zirconium alkyls or halides and also derivatives thereof, which are activated with the aid of aluminum, boron or phosphorus trialkyls or aluminoxane.
The practical use of these catalysts and related types in the wide variety of process variants developed can give products with sometimes very different properties. For olefin polymers, which are of generally known importance as materials, usability and field of use depend as a result of properties, on the one hand, on the type of monomers on which the polymer is based or on selection and ratio of the comonomers and the typical physical parameters characterizing the polymer, such as mean molecular weight, molecular weight distribution, degree of branching, degree of crosslinking, crystallinity, density, presence of functional groups in the polymer, etc., and, on the other hand, on properties determined by the process such as the content of low-molecular-weight impurities, presence of catalyst residues and finally on the costs.
To assess the performance of a coordination catalyst system, the decisive factors are, besides the realization of the desired product properties, further factors such as the activity of the catalyst system, i.e. the amount of catalyst required for an economical conversion of a given amount of olefin, the product throughput per unit time and the product yield, the loss of catalyst and also the reusability of the catalyst. Catalyst systems are therefore sought which have as high as possible a productivity but also have a high specificity in favor of a low degree of branching and a high stereo-regularity of the polymer, the latter being particularly important for polypropylene and polymers of higher 1-alkenes.
However, an essential question is also that of the stability and the handleability of the catalyst or its components. Pratically all known coordination catalysts are extremely sensitive to air and moisture. Exposure to (atmospheric) oxygen and/or water reduces or irreversibly destroys the activity of known coordination catalysts. Reduced Phillips catalysts, for example, immediately glow on exposure to air and are then unusable. The coordination catalysts therefore have to be strictly protected from exposure to air and moisture during preparation, storage and use, which naturally makes handling more difficult and increases the outlay required.
Conventional catalyst systems are also sensitive to materials which contain electron-rich elements such as oxygen or nitrogen. Compounds such as alcohols and amines, or even polar monomers which can be of interest as comonomers or additives for the polymer, deactivate the catalyst.
Even more sensitive in this respect and therefore even more difficult to handle are the organometallic compounds to be used as activators or cocatalysts, such as, in particular, the alkylaluminum compounds predominantly used for this purpose. Precisely these pose a serious problem in practice because of their extreme sensitivity and pyrophoric nature.
There was therefore a particular need to find less sensitive organometallic compounds which are nevertheless suitable as activating components in coordination catalyst systems. These substitute compounds should be able to make coordination catalyst systems having at least the same application properties and, if possible, an even greater breadth of use accessible. These themselves should in turn have a lower sensitivity and therefore less problematical handleability.